fix: de-specialize 3 arg mul!

src/Compiler.jl

@@ -105,7 +105,7 @@ function create_result(tocopy::D, path, result_stores) where {K,V,D<:AbstractDic
 end
 
 function create_result(
-    tocopy::Union{Integer,AbstractFloat,AbstractString,Nothing,Type,Symbol},
+    tocopy::Union{Integer,AbstractFloat,AbstractString,Nothing,Type,Symbol,Char},
     path,
     result_stores,
 )

src/Overlay.jl

@@ -119,24 +119,28 @@ end
 # LinearAlgebra.jl overloads
 ## `_mul!` goes through too many layers of abstractions and we aren't able to overload
 ## without specializing on every possible combination of types
-@reactant_overlay @noinline function LinearAlgebra.mul!(
-    C::AbstractVector, A::AbstractMatrix, B::AbstractVector, α::Number, β::Number
+for (cT, aT, bT) in (
+    (:AbstractVector, :AbstractMatrix, :AbstractVector),
+    (:AbstractMatrix, :AbstractMatrix, :AbstractVecOrMat),
 )
-    if any(Base.Fix2(isa, TracedRArray) ∘ ancestor, (C, A, B))
-        TracedLinearAlgebra.overloaded_mul!(C, A, B, α, β)
-    else
-        LinearAlgebra._mul!(C, A, B, α, β)
-    end
-    return C
-end
+    @eval begin
+        @reactant_overlay @noinline function LinearAlgebra.mul!(
+            C::$cT, A::$aT, B::$bT, α::Number, β::Number
+        )
+            if any(Base.Fix2(isa, TracedRArray) ∘ ancestor, (C, A, B))
+                TracedLinearAlgebra.overloaded_mul!(C, A, B, α, β)
+            else
+                LinearAlgebra._mul!(C, A, B, α, β)
+            end
+            return C
+        end
 
-@reactant_overlay @noinline function LinearAlgebra.mul!(
-    C::AbstractMatrix, A::AbstractMatrix, B::AbstractVecOrMat, α::Number, β::Number
-)
-    if any(Base.Fix2(isa, TracedRArray) ∘ ancestor, (C, A, B))
-        TracedLinearAlgebra.overloaded_mul!(C, A, B, α, β)
-    else
-        LinearAlgebra._mul!(C, A, B, α, β)
+        # Needed mostly for 1.10 where 3-arg mul is often specialized
+        @reactant_overlay @noinline function LinearAlgebra.mul!(
+            C::$cT, A::$aT, B::$bT
+        )
+            call_with_reactant(LinearAlgebra.mul!, C, A, B, true, false)
+            return C
+        end
     end
-    return C
 end

test/wrapped_arrays.jl

@@ -172,3 +172,33 @@ end
         @test all(iszero, y_res)
     end
 end
+
+function lower_triangular_write(x)
+    y = LowerTriangular(copy(x))
+    @. y *= 2
+    return y
+end
+
+function upper_triangular_write(x)
+    y = UpperTriangular(copy(x))
+    @. y *= 2
+    return y
+end
+
+function tridiagonal_write(x)
+    y = Tridiagonal(copy(x))
+    @. y *= 2
+    return y
+end
+
+@testset "Broadcasted Multiply and Alloate" begin
+    @testset "$(aType)" for (aType, fn) in [
+        ("LowerTriangular", lower_triangular_write),
+        ("UpperTriangular", upper_triangular_write),
+        ("Tridiagonal", tridiagonal_write),
+    ]
+        x = rand(4, 4)
+        x_ra = Reactant.to_rarray(x)
+        @test @jit(fn(x_ra)) ≈ fn(x)
+    end
+end